Method and device for monitoring the supply of substitution fluid during an extracorporeal blood treatment

ABSTRACT

The invention relates to a method for monitoring the supply of substitution liquid during an extracorporeal blood treatment and to an extracorporeal blood treatment unit equipped with a device for monitoring the supply of substitution liquid. The monitoring of the supply of substitution liquid is based on the measurement of pressure waves, which are generated by the substitution liquid pump, in the extracorporeal blood circulation system. A disturbance in the supply of substitution liquid is inferred when the amplitude of the pressure waves exceeds a predetermined limit value. The amplitude of the pressure waves is preferably monitored in the venous blood line.

FIELD OF THE INVENTION

The invention relates to a method for monitoring the supply ofsubstitution fluid during an extracorporeal blood treatment.Furthermore, the invention relates to equipment for extracorporeal bloodtreatment with a device for monitoring the supply of substitution fluid.

BACKGROUND OF THE INVENTION

In order to remove substances usually eliminated with urine and forfluid withdrawal, various methods for extracorporeal blood treatment orcleaning are used in chronic kidney failure. In haemodialysis, thepatient's blood is cleaned outside the body in a dialyser. The dialyserhas a blood chamber and a dialysis fluid chamber, which are separated bya semipermeable membrane. During the treatment, the patient's bloodflows through the blood chamber. In order to clean the blood effectivelyfrom substances usually eliminated with urine, fresh dialysis fluidflows continuously through the dialysis fluid chamber.

Whereas the transport of the low-molecular substances through themembrane is essentially determined by the concentration differences(diffusion) between the dialysis fluid and the blood in haemodialysis(HD), substances dissolved in the plasma water, in particularhigher-molecular substances, are effectively removed in haemofiltration(HF) by a high fluid flow (convection) through the membrane of thedialyser. In haemofiltration, the dialyser functions as a filter.Haemodiafiltration (HDF) is a combination of the two processes.

In haemo(dia)filtration, part of the serum drawn off through themembrane is replaced by a sterile substitution fluid, which is fed tothe extracorporeal blood circuit upstream of the dialyser (pre-dilution)or downstream of the dialyser (post-dilution).

Devices for haemo(dia)filtration are known in which the dialysis fluidis produced online from fresh water and concentrates and thesubstitution fluid is produced online from the dialysis fluid.

In known haemo(dia)filtration devices, the substitution fluid is fed tothe extracorporeal blood circuit from the fluid system of the machinevia a substitution fluid line. In pre-dilution, the substitution fluidline leads to a connection point on the arterial blood line upstream ofthe dialyser, whilst in post-dilution the substitution fluid line leadsto a connection point on the venous blood line downstream of thedialyser. The substitution fluid line has a connector, with which it canbe connected either to the venous or arterial blood line. In order tointerrupt the fluid supply, a clamp or suchlike is provided on thesubstitution fluid line.

The correct connection of the substitution fluid line is routinelychecked before the commencement of the blood treatment with knownhaemo(dia)filtration equipment. For this purpose, the line leading tothe dialysis fluid chamber and leading away from the dialysis fluidchamber of the dialyser and the venous blood line downstream of theconnection point for the substitution fluid line are clamped by means oftube clamps. The arterial blood line is already interrupted by thestationary blood pump upstream of the connection point for thesubstitution fluid line. The substituate pump for conveying thesubstitution fluid is then started, and the pressure in the venous bloodline is measured by means of a venous pressure sensor.

In the event that a pressure in the venous blood line cannot be built upwith the substituate pump that is greater than a preset limiting value,the conclusion is drawn that the connection of the substitution fluidline is not correct, i.e. the supply of fluid is interrupted. During theblood treatment, it can happen in dialysis practice that the treatmentprocedure is switched between post- and predilution. For this purpose,the clamp is closed on the substitution fluid line, and the substitutionfluid line is separated from the venous or arterial blood line andconnected to the arterial or venous blood line respectively. It cannotbe ruled out in practice that the opening of the tube clamp may beforgotten. If the substituate pump is not stopped and the pressure testdescribed above is not carried out, this state is not detected. It is adrawback that, with the known haemo(dia)filtration equipment, the supplyof substitution fluid is not monitored during the treatment. Aninterruption of the substituate supply, therefore, remains undetected.In this case, haemodialysis can be carried out with only little effectduring HDF treatment. During HF treatment, the patient is then nottreated at all in the extreme case. This can have more or less seriousconsequences for the patient, although he/she is not directlyendangered.

SUMMARY OF THE INVENTION

The problem underlying the invention is to provide a method such thatthe monitoring of the supply of substitution fluid during anextracorporeal blood treatment is also permitted when the treatmentprocedure is changed. A further problem underlying the invention is toprovide a device that also enables the monitoring of the substitutionfluid supply when the treatment procedure is changed. The solution tothese problems takes place according to the present invention.

The monitoring of the supply of substitution fluid is based on the factthat the amplitude of the pressure waves of the substituate pump ismonitored in the fluid system or extracorporeal blood circuit. It hasbeen shown that a malfunction of the substitution fluid supply ispresent when the amplitude of the pressure waves exceeds a presetlimiting value.

The method according to the invention and the device according to theinvention require that the substituate pump for conveying thesubstitution fluid is a pump generating pressure waves, in particular avolumetric occlusion pump (roller pump).

The pressure waves emerging from the substituate pump are able topropagate via the fluid system of the extracorporeal blood treatmentequipment through the dialyser into the extracorporeal blood circuit.This path is open even when the substitution fluid supply isinterrupted. The substituate pump then operates against the closure. Theamplitude of the pressure waves, which can be detected in theextracorporeal blood circuit, thus increases.

In an embodiment of the invention, the amplitude of the pressure wavesis measured in the extracorporeal blood circuit downstream of thedialyser. This has the advantage that a pressure sensor can be used thatis in any case provided in the venous blood line in the known bloodtreatment equipment.

In another embodiment of the invention, the amplitude of the pressurewaves is measured in the fluid system upstream of the dialyser orfilter. This has the advantage that monitoring is also possible duringoperation of the blood treatment equipment as haemofiltration equipment,in which the pressure waves cannot reach the extracorporeal circuitsince the inlet of the dialyser or filter is cut off from the dialysisfluid supply.

The pressure signal is preferably filtered with a bandpass in order toeliminate disturbing pulses, whereby the amplitude of the filteredpressure signal is then compared with the preset limiting value.

It has been shown that the enlargement of the amplitude of the pressurewaves is dependent on the pumping rate (speed) of the substituate pump.A false alarm can be eliminated by the fact that, when the presetlimiting value is exceeded, the conclusion is drawn that there is amalfunction only if the pumping rate lies between preset limitingvalues. These limiting values should be rated in such a way that thechange in amplitude traceable to the changes in the pumping rate issmaller than the change in amplitude due to an interruption of thesubstitution fluid supply.

An acoustic and/or optical alarm is expediently emitted when the presetlimiting value is exceeded. Action by the operator in the control of theblood treatment equipment can however also be taken.

The monitoring device of the extracorporeal blood treatment equipmenthas means for monitoring the amplitude of the pressure waves of thesubstituate pump in the fluid system, preferably upstream of thedialyser or filter, or in the extracorporeal blood circuit, preferablydownstream of the dialyser or filter, and means for evaluating thepressure-wave amplitude. The substituate pump generating pressure wavesis arranged in the substitution fluid line, which leads from the fluidsystem to the blood circuit upstream or downstream of the dialyser orfilter. The substitution fluid line can be a single tube line or also atube-line system with several branches.

The only decisive factor is that a flow connection is created betweenthe fluid system and the blood circuit of the blood treatment equipment.

The substitution fluid line can be connected directly to the venous orarterial blood line. It is however also possible for the line to beconnected to drip chambers or suchlike, which are provided in the venousor arterial blood line.

The fluid system of the blood treatment equipment can include a dialysisfluid supply line leading to the dialysis fluid chamber of the dialyserand a dialysis fluid discharge line leading away from the dialysis fluidchamber of the dialyser. One or more filters can be arranged in thefluid system in order to increase safety. Further lines, for examplebypass lines etc., can also be provided. The only decisive factor is thefact that the fluid system permits a propagation of pressure waves, i.e.is a system completely filled with a medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows equipment for extracorporeal blood treatment with a devicefor monitoring the supply of substitution fluid in a greatly simplifydiagrammatic representation.

FIG. 2 shows the filtered venous pressure signal as a function of timein post-dilution (FIG. 2A), disconnection (FIG. 2B) and pre-dilution(FIG. 2C), when the pumping rate of the substituate pump amounts to 20ml/min.

FIG. 3 shows the filtered venous pressure signal as a function of timein post-dilution (FIG. 3A), disconnection (FIG. 3B) and pre-dilution(FIG. 3C), with a substituate pumping rate of 60 ml/min.

FIG. 4 shows the filtered venous pressure signal as a function of timein post-dilution (FIG. 4A), disconnection (FIG. 4B) and pre-dilution(FIG. 4C), with a substituate pumping rate of 100 ml/min.

DETAILED DESCRIPTION

An exemplary embodiment of the invention will be explained in greaterdetail below by reference to the drawings.

FIG. 1 shows a simplified diagrammatic representation of the essentialcomponents of haemo(dia)filtration equipment together with a device formonitoring the supply of substitution fluid from the fluid system of thehaemo(dia) filtration equipment in the extracorporeal blood circuit.

The haemo(dia) filtration equipment has a dialyser or filter 1, which isseparated by a membrane 2 into a first chamber 3 through which bloodflows and a second chamber 4 through which dialysis fluid flows. Firstchamber 3 is connected into an extracorporeal blood circuit 5A, whilstsecond chamber 4 is connected into fluid system 5B of thehaemo(dia)filtration equipment.

Extracorporeal blood circuit 5A includes an arterial blood line 6, whichleads to inlet 3 a of blood chamber 3, and a venous blood line 7, whichleads away from outlet 3 b of blood chamber 3 of dialyser 1. In order toeliminate air bubbles, an arterial drip chamber 8 is connected intoarterial blood line 6 and a venous drip chamber 9 is connected intovenous blood line 7. The patient's blood is conveyed through the bloodchamber of the dialyser by means of an arterial blood pump 10, inparticular a roller pump, which is arranged on arterial blood line 6.

Fluid system 5B includes a dialysis fluid supply line 11, which leads toinlet 4 a of dialysis fluid chamber 4, and a dialysis fluid dischargeline 12, which leads away from outlet 4 b of dialysis fluid chamber 4 ofdialyser 1. Fresh dialysis fluid flows from a dialysis fluid source (notshown) into the dialysis fluid chamber via dialysis fluid supply line11, whilst the used dialysis fluid is discharged from the dialysis fluidchamber via dialysis fluid discharge line 12 to a discharge (not shown).The balancing device for balancing fresh against used dialysis fluid, asgenerally provided in haemo(dia)filtration equipment, has not beenrepresented for the sake of better clarity. Additional equipment forcleaning and rinsing the system are likewise not represented.

Dialysis fluid supply line 11 includes a first section 11 a, which leadsto inlet 13 a of a first chamber 13 of a sterile filter 16, subdividedby a membrane 14 into the first chamber and a second chamber 15, and asecond section 11 b, which runs away from outlet 13 b of first chamber13 of filter 16 and leads to inlet 4 a of dialysis fluid chamber 4.

During the dialysis treatment, dialysis fluid can be fed from fluidsystem 5B as substitution fluid via tube line 17 to extracorporeal bloodcircuit 5A. Substitution fluid line 17 has at both ends two linesections 17 a, 17 b, 17 c, 17 d respectively. Line section 17 a isconnected with a first outlet 15 a and line section 17 b with a secondoutlet 15 b of second chamber 15 of sterile filter 16, whilst aconnector 18 a, 18 b is connected respectively to line sections 17 c and17 d. With the two connectors 18 a, 18 b, substitution fluid line 17 isconnected to a connection line 19 leading to arterial drip chamber 8 anda connection line 20 leading to venous drip chamber 9. Connection lines19, 20 have corresponding connection pieces 19 a, 20 a for this purpose.There are provided on line sections 17 c and 17 d tube clamps 35, 36,with which a fluid connection can optionally be created with connectionline 19 or 20 in order to undertake a pre- or post-dilution. A branchcan however also be dispensed with if a tube clamp is provideddownstream of substituate pump 22 for the purpose of clampingsubstitution fluid line 17. It is then necessary, however, to exchangethe line connections manually.

The substitution fluid is conveyed by means of an occlusion pump, inparticular roller pump 22, into which substitution fluid line 17 isinserted. Such roller pumps belong to the prior art. They have severalrollers 22 a, 22 b, with which the cross-section of the tube line forconveying the fluid is reduced. As a result, pressure waves arise whichcan be propagated in both directions via the substitution fluid line. AHall sensor 23, which measures the pumping rate, is provided onsubstituate pump 22.

In order to measure the pressure in venous blood line 7, a pressuresensor 24 is provided, which is connected via a pressure line 25 tovenous drip chamber 9. The pressure sensor delivers an electrical signalproportional to the pressure in the venous blood line.

For the operation of the haemo(dia)filtration equipment as haemodialysisequipment, tube clamps 35, 36 are closed, so that dialysis fluid flowsthrough dialysis fluid chamber 4 of the dialyser. For the operation ofthe haemo(dia)filtration equipment as haemodiafiltration equipment, tubeclamp 35, 36 is opened, so that sterile dialysis fluid as substitutionfluid flows from sterile filter 16 into venous drip chamber 8(pre-dilution) or arterial drip chamber 9 (post-dilution). Operation ofthe haemo(dia)filtration equipment solely as haemofiltration equipmentis however also possible if the supply of dialysis fluid into dialysisfluid chamber 4 of dialyser 1 is interrupted. In order to interrupt thefluid supply, a shut-off device 26 is provided upstream of dialyser 1.

Venous pressure sensor 24 is connected to a signal line 28 with abandpass filter 29. Bandpass filter 29 is in turn connected to a dataline 30 with an evaluation unit 31, which receives an electrical signaldependent on the pumping rate of substituate pump 22 via a furthersignal line 34 of Hall sensor 23.

Evaluation unit 31 determines the amplitude of the pressure signalfiltered with bandpass filter 29 and compares the amplitude with apreset limiting value. 1.5 to 2.5 times, preferably 1.8 to 2.2 times, inparticular 2.0 times the amplitude of the pressure waves measured duringtrouble-free operation is adopted as the preset limiting value.

In the event that, following a change of the treatment, for example frompre- to post-dilution, the opening of tube clamps 35, 36 is forgotten,i.e. substitution fluid line 17 is clamped, the amplitude of thepressure signal increases sharply.

FIGS. 2A, 2B and 2C show the filtered venous pressure signal togetherwith the periodic signal of the Hall sensor as a function of time with asubstituate pumping rate of 20 ml/min. for the cases of post-dilution(A), disconnection (B) and predilution (C). Blood and dialysate flow areset at 300 ml/min. The following values result:Ampl_(post)=1.5 V; Ampl_(discon)=3.0 V; Ampl_(pre)=1.5 V.Ampl_(discon)/Ampl_(post)=2.0; Ampl_(discon)/Ampl_(pre)=2.0

It emerges that the amplitude of the pressure waves is doubled when thesubstitution fluid flow is interrupted. Therefore, when the evaluationunit establishes that the pressure amplitude is greater than the presetlimiting value, for example 2.0 times the normal value, the evaluationunit generates an alarm signal, which is received by an alarm unit 32via an alarm line 33. Alarm unit 32 then emits an acoustic and/oroptical alarm.

FIGS. 3A, 3B and 3C show the filtered venous pressure signal and theHall signal as a function of time with a higher pumping rate of 60ml/min. with post-dilution (A), disconnection (B) and pre-dilution (C).Blood and dialysate flow are again 300 ml/min. The following valuesresult:Ampl_(post)=1.9 V; Ampl_(discon)=3.6 V; Ampl_(pre)=1.8 V.Ampl_(discon)/Ampl_(post)=1.9; Ampl_(discon)/Ampl_(pre)=2.0

The filtered venous pressure signal and the Hall signal with a stillhigher pumping rate of 100 ml/min. with post-dilution (A), disconnection(B) and pre-dilution (C) is shown in FIGS. 4A, 4B and 4C. Blood anddialysate flow are again 300 ml/min. The following values result:Ampl_(post)=1.7 V; Ampl_(discon)=3.2 V; Ampl_(pre)=1.7 V.Ampl_(discon)/Ampl_(post)=1.9 Ampl_(discon)/Ampl_(pre)=1.9

Concerning the amplitude values of FIGS. 2 and 3, it should be notedthat the measured values have been adapted in order to have comparablemagnitudes. In practice, the increase in the pressure amplitude when theflow of substitution fluid is interrupted is not independent of thepumping rate.

In order to increase safety, a false alarm can be eliminated by the factthat the pumping rate is also taken into account in the comparison ofthe measured pressure signal with the preset limiting value. For thispurpose, evaluation unit 31 also receives the signal of Hall sensor 23.

As long as the pumping rate lies between preset limits, the evaluationunit assumes that an increase in the pressure amplitude is a consequenceof an interruption of the substitution fluid supply. For example,Ampl_(after)/Ampl_(before)>1.5 can be adopted as the limiting value. Thethreshold value needs to be correspondingly corrected for higher pumpingrates. This can take place by the fact that different threshold valuesare adopted for different pumping rate ranges.

The increase of the pressure amplitude can be traced back to thefollowing. In the case of a blockage of the supply of substitutionfluid, the spring forces of the rotor of roller pump 22 are no longercapable of compressing substitution fluid tube 17, so that the maximumsystem pressure is reached. This pressure, which is also referred to asthe occlusion pressure, is much higher than the normal system pressure.The rotor thus delivers against the higher occlusion pressure in thecase of a substitution fluid blockage. On account of closed tube clamp35 and 36 respectively, the transmission path of the pressure waves viasubstitution fluid tube 17 to venous pressure sensor 24 is completelyblocked. The pressure waves generated by substituate pump 22 reachvenous pressure sensor 24, however, via sterile filter 16, secondsection 11 b of the dialysis fluid supply line, dialyser 1, venous bloodline 7, venous drip chamber 9 and finally pressure line 25. As FIGS. 2to 4 show, the amplitude of the pressure signal is doubled at the timeof disconnection on account of the raised occlusion pressure.

In another embodiment of the invention, the pressure waves are monitorednot in the extra corporeal blood circuit (5A), but in the fluid system(5B) of the blood treatment equipment upstream of dialyser 1 or of thefilter. This form of embodiment differs from the example of theembodiment described above in that pressure sensor 24 is not provided invenous blood line 7, but rather a pressure sensor 24′ is provided insecond section 11 b of the dialysis fluid supply line. This pressuresensor 24′ is indicated in FIG. 1 with dashed lines as an alternativeform of embodiment. It is connected with low-pass filter 29 via signalline 28′ also indicated with dashed lines. The pressure waves canhowever also be measured at another point of the fluid system.

1-16. (canceled).
 17. A method for monitoring the supply of asubstitution fluid during an extracorporeal blood treatment with anextracorporeal blood circuit, wherein the extracorporeal blood circuitincludes a first chamber of a dialyser or a filter, wherein the dialyseror the filter is subdivided by a semipermeable membrane into the firstchamber and a second chamber, and with a fluid system which includes thesecond chamber of the dialyser or the filter, the method comprising:feeding the substitution fluid from the fluid system to theextracorporeal blood circuit upstream or downstream of the dialyser orthe filter by operation of a substituate pump which generates pressurewaves; and monitoring the amplitude of the pressure waves in the fluidsystem or in the extracorporeal blood circuit generated by thesubstituate pump, wherein a malfunction of the supply of thesubstitution fluid is indicated by the amplitude of the pressure wavesexceeding a preset limiting value.
 18. The method according to claim 17,wherein the substitution fluid is fed downstream of the dialyser or thefilter, and the amplitude of the pressure waves is monitored in theextracorporeal blood circuit.
 19. The method according to claim 17,wherein the substitution fluid is fed upstream of the dialyser or thefilter, and the amplitude of the pressure waves is monitored in thefluid system.
 20. The method according to claim 17, further comprising:monitoring a pumping rate of the substituate pump, wherein a malfunctionof the supply of the substitution fluid is indicated by the amplitude ofthe pressure waves exceeding a preset limiting value only if the pumpingrate lies between a second preset limiting value and a third presetlimiting value.
 21. The method according to claim 17, furthercomprising: measuring a pressure signal in the extracorporeal bloodcircuit; and filtering the pressure signal with a bandpass, wherein theamplitude of the filtered pressure signal is compared with the presetlimiting value.
 22. The method according to claim 17, furthercomprising: emitting at least one of an acoustic alarm and an opticalalarm when the preset limiting value is exceeded.
 23. The methodaccording to claim 17, wherein the substituate pump is a roller pump.24. The method according to claim 17, wherein the monitoring of thesupply of the substitution fluid occurs continuously during theextracorporeal blood treatment.
 25. The method according to claim 17,wherein the monitoring of the supply of the substitution fluid takesplace continuously during the operation of the substituate pump.
 26. Anapparatus for extracorporeal blood treatment comprising: anextracorporeal blood circuit including a first chamber of a dialyser ora filter, wherein the dialyser or the filter is subdivided by asemipermeable membrane into the first chamber and a second chamber; afluid system including the second chamber of the dialyser or the filter;a substitution fluid line leading from the fluid system to theextracorporeal blood circuit upstream or downstream of the dialyser orthe filter, wherein a substituate pump generating pressure waves isarranged in the substitution fluid line; and a monitoring device formonitoring a supply of substitution fluid from the fluid system into theextracorporeal blood circuit, wherein the monitoring device includesmeans for monitoring the amplitude of the pressure waves in the fluidsystem or in the extracorporeal blood circuit generated by thesubstituate pump, and means for evaluating the amplitude of the pressurewaves, wherein the monitoring device is designed such that a malfunctionof the supply of substitution fluid is indicated by the amplitude of thepressure waves exceeding a preset limiting value.
 27. The apparatusaccording to claim 26, wherein the means for monitoring the amplitude ofthe pressure waves generated by the substituate pump are arranged in theextracorporeal blood circuit downstream of the dialyser or the filter.28. The apparatus according to claim 26, wherein the means formonitoring the amplitude of the pressure waves generated by thesubstituate pump are arranged in the-fluid system upstream of thedialyser or the filter.
 29. The apparatus according to claim 26, furthercomprising: means for monitoring a pumping rate of the substituate pump,wherein a malfunction of the supply of the substitution fluid isindicated by the amplitude of the pressure waves exceeding a presetlimiting value only if the pumping rate lies between a second presetlimiting value and a third preset limiting value.
 30. The apparatusaccording to claim 27, further comprising: means for monitoring apumping rate of the substituate pump, wherein a malfunction of thesupply of the substitution fluid is indicated by the amplitude of thepressure waves exceeding a preset limiting value only if the pumpingrate lies between a second preset limiting value and a third presetlimiting value.
 31. The apparatus according to claim 28, furthercomprising: means for monitoring a pumping rate of the substituate pump,wherein a malfunction of the supply of the substitution fluid isindicated by the amplitude of the pressure waves exceeding a presetlimiting value only if the pumping rate lies between a second presetlimiting value and a third preset limiting value.
 32. The apparatusaccording to claim 26, wherein the means for monitoring the amplitude ofthe pressure waves generated by the substituate pump include a pressuresensor for measuring a pressure in the extracorporeal blood circuitdownstream of the dialyser or the filter, a pressure signal sensor forgenerating a pressure signal dependent on the measured pressure, and abandpass filter for filtering the pressure signal.
 33. The apparatusaccording to claim 27, wherein the means for monitoring the amplitude ofthe pressure waves generated by the substituate pump include a pressuresensor for measuring a pressure in the extracorporeal blood circuitdownstream of the dialyser or the filter, a pressure signal sensor forgenerating a pressure signal dependent on the measured pressure, and abandpass filter for filtering the pressure signal.
 34. The apparatusaccording to claim 28, wherein the means for monitoring the amplitude ofthe pressure waves generated by the substituate pump include a pressuresensor for measuring a pressure in the extracorporeal blood circuitdownstream of the dialyser or the filter, a pressure signal sensor forgenerating a pressure signal dependent on the measured pressure, and abandpass filter for filtering the pressure signal.
 35. The apparatusaccording to claim 26, further comprising: an alarm unit for generatingat least one of an acoustic alarm and an optical alarm when the presetlimiting value is exceeded.
 36. The apparatus according to claim 26,wherein the substituate pump is a roller pump.